Accumulator charging circuit for high pressure hydraulic system

ABSTRACT

An accumulator charging arrangement for a high pressure hydraulic system. The arrangement includes a pair of relatively small volumetric capacity fixed-displacement pumps each of which is combined with a separate accumulator charging valve. The pumpcharging valve combinations are disposed in parallel to feed pressure fluid to a pair of accumulator devices for use of the hydraulic circuit upon specific demand. One pump-charging valve combination supplies pressure fluid only within a certain pressure range. The second pump-charging valve combination supplies fluid at a second discrete pressure range which is higher than that within which the first combination operates. For system demands within a lower pressure range, both pump-charging valve combinations are operative to supply fluid, however, upon a demand for pressure only within the higher pressure range, only the second pump-valve combination is operative to supply the separate accumulator devices associated with the combinations.

United States Patent [191 J unck et al.

1 1 Nov. 11, 1975 1 ACCUMULATOR CHARGING CIRCUIT FOR HIGH PRESSUREHYDRAULIC SYSTEM [75] Inventors: John A. Junck; Howard L. Johnson,

both of Joliet, ll].

[73] Assignee: Caterpillar Tractor Company,

Peoria, 111.

[22] Filed: Feb. 6, 1974 [21] Appl. N0.: 440,145

[52] US. Cl. 417/288; 60/416; 60/418;

Primary Examiner-C. J. Husar Assistant Examiner-Leonard Smith Attorney,Agent, or Firm-Phillips, Moore, Weissenberger, Lempio & Strabala [57]ABSTRACT An accumulator charging arrangement for a high pressurehydraulic system. The arrangement includes a pair of relatively smallvolumetric capacity fixeddisplacement pumps each of which is combinedwith a separate accumulator charging valve. The pump charging valvecombinations are disposed in parallel to feed pressure fluid to a pairof accumulator devices for use of the hydraulic circuit upon specificdemand. One pump-charging valve combination supplies pressure fluid onlywithin a certain pressure range. The second pump-charging valvecombination supplies fluid at a second discrete pressure range which ishigher than that within which the first combination operates. For systemdemands within a lower pressure range, both pump-charging valvecombinations are operative to supply fluid, however, upon a demand forpressure only within the higher pressure range, only the secondpump-valve combination is operative to supply the separate accumulatordevices associated with the combinations.

2 Claims, 1 Drawing Figure US. Patent Nov. 11, 1975 3,918,847

TO BRAKES ACCUMULATOR CHARGING CIRCUIT FORHIGH PRESSURE HYDRAULIC SYSTEMBACKGROUND or THE INVENTION This invention relates to an accumulatorcharging circuit which includes a pair of fixed-displacement pumps incombination with a pair of' accumulator charging valves for chargingseparate accumulator means to provide a system which simulates avariabledisplacement pump arrangement for charging of one or moreaccumulators in a hydraulic system.

Earthmoving vehicles, such as motor graders and the like, commonlyemploy accumulators in their hydraulic systems to ensure a constantsupply of working fluid for actuating various fluid operated components,such as brakes, steering, and the like. Since the output of an enginedriven pump varies with the speed of the vehicle engine, pumps chosen inprior art systems had to have volumetric capacities sufficiently largeto ensure that the required volume would be available to the accumulatorcircuit even at minimum pumping rates.

In the past, a single fixed-displacement pump and an accumulatorcharging valve were utilized to charge the accumulator of such hydraulicsystems. It is obvious that such pumps operated much of the time with avolumetric output in excess of that required'by the accumulator circuit.This is so because sucha pump, as mentioned above, had to be largeenough to handlethe largest capacity requirements demanded. With suchlarge capacity pumps charging prior art accumulators, considerablehorsepower had to be diverted from the vehicle engine for pump actuationand this resulted in a loss of power to perform other usefulwork. Such.diversion of power is particularly undesirable in vehicles such as motorgraders because the intermittent lugging of the grader engine due toon'and off cycling of the pump makes critical handling and controlfunctions difficult to perform. I

One rather effective solution to the problem has been the utilization ofa variable displacement pump such as that shown in U.S. Pat. applicationSer. No. 373,612, filed by Hein, et al., of common assignment herewith.Unfortunately the substitution of a variable displacement pump in asystem normally utilizing a--fixeddisplacement pumps is not alwayspractical due to the relative complexity and expense of thevariabledisplacement pump.

Additional prior art systems utilizing variable displacement means areshown in U.S. Pat. applications Ser. Nos. 283,855 to Hein, et al., and272,408 to Ferre, et al., both of common assignment herewith.

SUMMARY AND OBJECTS OF THE INVENTION The instant invention provides anaccumulator charging arrangement for a hydraulic system utilizing aplurality of fixed-displacement pumps having relatively small capacitiesand being individually operative only upon specific system demands. Eachpump is combined with an accumulator charging valve which providesoperating fluid to an accumulator device within a given predeterminedpressure range. At low volume, high pressure system demands only one ora few pumpcharging valve combinations will be operative, whereas atmaximum volume, low pressure demands, all pumpvalve combinations will beoperative to supply the accumulator means.

The main object of the present invention is to provide a chargingarrangement for the accumulators of a hydraulic system which arrangementdoes not utilize expensive variable -displacement pumps.

Another object of the invention is to provide a system utilizing aplurality of fixed-displacement pumps connected in parallel to'provideindividual or combined flow to meet specific system requirements.

A still further object of the present invention is to provide aplurality offixed-displacement pumps each arranged in a parallel circuitwith an accumulator charging valve and a separate'accumulator device andoperated upon demand to charge the respective accumulators. I

Other objects-and advantages of the invention will become apparent fromthe following description and drawing.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE of the drawing is apartially schematic representation of the instant accumulator chargingarrangment shown coupled to hydraulic user circuitry of a gradervehicle.

DETAILED DESCRIPTION With reference to the drawing, the preferredembodiments of the instant charging arrangement are shown generally at10. The arrangement is shown in association with a hydraulic system,shown generally at 12, for a motor grader not shown. The particularhydraulic system illustrated is supplied by two parallel circuits 14 and16. The circuit 14 includes, in series, a check valve 22, an accumulator24, and a priority valve 26. This circuit is adapted tosu'pply pressurefluid to a brake valve 18 and an implement valve 20. The priority valvegives priority to the brake valve 18 over the implement valve 20. Thecircuit 16 supplies fluid under pressure to a steering valve 28 andincludes, in series, a check valve 30, an accumulator '32, and areducing valve 34.

Both circuitsare uniformly'supplied with fluid under pressure from theaccumulator charging circuit 10 of the presentinvention. The circuitincludes a pair of accumulator charging valves 36 and 38 disposed in aparallel with respect to the user circuit. The accumulator chargingvalves utilized in the preferred embodiment are essentially identical tothe valve assembly fully disclosed in U.S. Pat. No. 3,570,519, toBianchetta, of common assignment herewith, and will not be discussed indetail herein. The valve 36 functions to charge in a high pressurerange, for example from 3,100 to 3,500 psi, whereas the valve 38functions to charge in a lower pressure range, on the order of 2,700 to3,100 psi.

The charging circuit also includes a relatively small capacity fixeddisplacement pump 40 for supplying fluid under pressure to the highrange accumulator valve 36, and a relatively large capacity constantdisplacement pump 42, for supplying fluid to the lower range accumulatorcharging valve 38. In a typical example, the pump 40 would have acapacity of 15 gallons per minute while the pump 42 would provide some25 gallons per minute.

In operation, when the pressure in either or both of the accumulators 24or 32 falls below 2,700 psi, i.e.,

the minimum charging pressure of the accumulator charging valves 36 and38, fluid under pressure from both of the pumps 40 and 42 would bedirected to the accumulators 24 and 32. Upon reaching the maximumcharging pressure of the valve 38, i.e., 3,100 psi, such valve will dumpfluid pumped by the larger capacity pump 42 to a tank 11 through a line39 in the manner disclosed particularly in the above-mentioned patent toBianchetta. The smaller capacity pump 40 will continue to charge boththe accumulators until a maximum pressure of 3,500 psi is reached,whereupon the accumulator charging valve 36 will cease charging and willdump the excess output of the smaller pump to the tank 11 through anoutlet line 37.

During operation of the vehicle, the accumulator pressure willfrequently drop below 3,100 psi due to the use of the various of thecontrol valves 18, and 28. When this occurs, the charging valve 36 willautomatically shift to redirect fluid from the smaller capacity pump 40to the accumulators. The larger pump 42 will be utilized only to chargethe accumulators during periods of extreme fluid demand when systempressure would tend to drop grossly. Consequently, it will beappreciated that substantial savings in engine horsepower may berealized by charging with only the smaller capacity pump during mostvehicle operations and by utilizing the larger capacity pump 42 only atsuch times as is necessary as determined by the flow requirements of thesystem. It is also obvious that it is preferable to have a small lowcapacity pump cutting on and off instead of a larger one, which wouldlug the engine during charging and interfere with ancillary control andimplement functions.

While the invention has been described with reference to the preferredembodiments thereof, it is apparent that the variations andmodifications are possible within the purview of the inventive concepts.No limitation with respect to such variations and modifications isintended, except by the scope of the appended claims.

We claim:

1. An accumulator charging system for charging accumulator means whichsupply fluid under pressure to a fluid user circuit, said systemcomprising; accumulator means, a source of fluid, first pump means influid communication with said source, first fluid communication meansfor communicating the output of said first pump means with saidaccumulator means, said first pump means having a fixed displacement andmaximum pumping capacity of a first predetermined value, first automaticcharging valve means in said first fluid communication means forcontrolling the flow of fluid from said first pump means to saidaccumulator means, said first automatic charging valve means beingresponsive to the pressure extant in said accumulator means forpermitting fluid flow from said first pump means to said accumulatormeans only when the pressure within said accumulator means is within afirst predetermined range of positive pressures and for returning fluidfrom said first pump means to said source when said accumulator meanspressure is above said first predetermined range of pressures, secondpump means in communication with said source, second fluid communicationmeans for communicating the output of said sec- 0nd pump means with saidaccumulator means, second automatic charging valve means in said secondfluid communication means for controlling the flow of fluid from saidsecond pump means to said accumulator means, said second pump meanshaving a fixed dis placement and constant volumetric capacity of a givensecond predetermined value which is less than said first predeterminedvalue, said second automatic charging valve means permitting fluid flowfrom said second pump means to said accumulator means when the pressureextant in said accumulator means is within a second predetermined rangeof positive pressures extending to a higher pressure than said firstpredetermined range of pressures, said second charging valve means beingeffective to return fluid from said second pump means to said sourcewhen accumulator pressure rises above the maximum pressure of saidsecond predetermined range of pressures, said accumulator meansincluding first and second fluid accumulator devices each saidaccumulator device being connected for fluid communication with both ofsaid first and second automatic charging valve means at least partiallythrough common conduit means, first check valve means in said firstfluid communication means between said common conduit means and saidfirst accumulator device for permitting flow from said first chargingvalve means to said first accumulator device but preventing reverseflow.

2. The invention of claim 1 including second check valve means in saidsecond fluid communication means between said common conduit means andsaid second accumulator device for permitting flow from said secondcharging valve means to said second accumulator device but preventingreverse flow.

1. An accumulator charging system for charging accumulator means whichsupply fluid under pressure to a fluid user circuit, said systemcomprising; accumulator means, a source of fluid, first pump means influid communication with said source, first fluid communication meansfor communicating the output of said first pump means with saidaccumulator means, said first pump means having a fixed displacement andmaximum pumping capacity of a first predetermined value, first automaticcharging valve means in said first fluid communication means forcontorlling the flow of fluid from said first pump means to saidaccumulator means, said first automatic charging valve means beingresponsive to the pressure extant in said accumulator means forpermitting fluid flow from said first pump means to said accumulatormeans only when the pressure within said accumulator means is within afirst predetermined range of positive pressures and for returning fluidfrom said first pump means to said source when said accumulator meanspressure is above said first predetermined range of pressures, secondpump means in communication with said source, second fluid communicationmeans for communicating the output of said second pump means with saidaccumulator means, second automatic charging valve means in said secondfluid communication means for controlling the flow of fluid from saidsecond pump means to said accumulator means, said second pump meanshaving a fixed displacement and constant volumetric capacity of a givensecond predetermined value which is less than said first predeterminedvalue, said second automatic charging valve means permitting fluid flowfrom said second pump means to said accumulator means when the pressureextant in said accumulator means is within a second predetermined rangeof positive pressures extending to a higher pressure than said firstpredetermined range of pressures, said second charging valve means beingeffective to return fluid from said second pump means to said sourcewhen accUmulator pressure rises above the maximum pressure of saidsecond predetermined range of pressures, said accumulator meansincluding first and second fluid accumulator devices each saidaccumulator device being connected for fluid communication with both ofsaid first and second automatic charging valve means at least partiallythrough common conduit means, first check valve means in said firstfluid communication means between said common conduit means and saidfirst accumulator device for permitting flow from said first chargingvalve means to said first accumulator device but preventing reverseflow.
 2. The invention of claim 1 including second check valve means insaid second fluid communication means between said common conduit meansand said second accumulator device for permitting flow from said secondcharging valve means to said second accumulator device but preventingreverse flow.